In recent years bicycling has become a very popular recreational and physical-conditioning activity. In one form of recreational bicycling, bicycle touring, it is desirable to equip the bicycle with a rear carrier rack and to use rear carrier rack panniers to carry clothing, food, camping equipmet and the like. Most panniers presently available are lightweight flexible bags which are hung by straps or hooks from the side bars of the rear rack, and although they are gnerally satisfactory if carefully packed, they have only moderate shape stability and are prone to distorting under load, even to the point in extreme cases of careless use of interfering with the rear wheel. A few panniers having internal frames have been marketed, but they have not eliminated the problems that often arise from improper packing.